In a magnetic disk apparatus, when an amount of an offtrack of a magnetic head from the target track in the radial direction exceeds a predetermined value during data recording, there is the possibility that a part of the data of the neighboring track is erased and the information of the neighboring track cannot be read.
In a conventional magnetic disk apparatus using an embedded servo system including a data recording area and servo information for a recording track on a magnetic disk medium, a track position signal is demodulated from reproduced servo information during data writing and writing in the state of offtrack is prevented by monitoring the amount of offtrack during writing. Namely, an art for prohibiting the write operation is used when the amount of offtrack of the magnetic head in the direction of track width immediately before writing or during writing is more than a preset value.